JP3105277B2 - Axial gas turbine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial gas turbine having a multi-stage turbine for driving a compressor arranged on a common shaft. The shaft portion is configured as a drum surrounded by a drum cover, and cooling air recovered from the compressor is transferred to and at the end face of the turbine rotor by an annular passage formed between the drum and the drum cover. It is then directed towards a cooling passage on the rotor side of the turbine rotor, in order to seal between the pressure level at the outlet of the compressor and the pressure level at the inlet of cooling air into the turbine. A labyrinth seal that exerts a sealing action on the drum cover is arranged on the drum,
In this case, it relates to a type in which the entire cooling air on the rotor side for the turbine is recovered from the compressor in the region of the compressor outlet.

[0002]

2. Description of the Prior Art Gas turbines of the above type are known.
The entire cooling air on the rotor side is recovered from the collection chamber between the compressor and the turbine. That is, most of the cooling air flows directly into the rotor cooling passage via the acceleration grid. In this case, the acceleration grid is usually provided on the end face of the turbine rotor on the same radius as the rotor cooling passage.

[0003] A small portion of the cooling air, the air needed to cool the last compressor disk and the drum and the first turbine disk, is used to obtain a cooling effect.
Before the cooling air is introduced into the annular passage without creating a swirling flow, it must be recooled in the cooler. Such an arrangement creates a number of disadvantages.

[0004] In other words, in one aspect, the cooling air to be recovered from the collection chamber does not have the desired desired purity as best as a particularly narrow blade cooling passage is desired.

[0005] On the other hand, separate and expensive equipment is required for recooling.

In addition, a small amount of air to be recooled is heated considerably again before flowing into the annular passage by convective heating, whereby the cooling effect is reduced.

In addition, the introduction of air without creating a swirling flow additionally increases the temperature of the adiabatic wall in this range.

Furthermore, the introduction of cooling air into the annular passage without creating swirling flow results in a high heat transfer coefficient α over the entire rotor range to be loaded, thereby contributing to the increased cooling temperature mentioned above. High transient stresses occur.

In addition, an excessively high heat transfer coefficient α occurs with known disadvantages in the labyrinth seal area of the drum.

In the case of known gas turbines, backflow is conscious, that is to say that recooled air flows from the annular passage behind the last bucket row of the compressor into the main passage of the compressor. I have. This action creates major obstacles to the mainstream.

By forcing the rotor into the cooling passage with a slight swirling flow, the rotor must perform a pumping operation, which further increases the cooling air temperature.

[0012]

SUMMARY OF THE INVENTION The object of the present invention is to avoid all of the disadvantages mentioned above and to provide an axial-flow gas turbine of the type mentioned at the outset with a large-sized designed rotor end face on the turbine side. At the same time to reduce axial thrust.

[0013]

SUMMARY OF THE INVENTION According to the present invention, there is provided, in accordance with the present invention, cooling air on the rotor side for a turbine, which is recovered at the compressor boss behind the last rotor row of the compressor and provided to the cooling air. Swirling flow is introduced directly into the annular passage, and this cooling air is deflected in the swirl grid inside the annular passage and accelerated to near the speed of sound Solved.

[0014]

The advantages of the invention are, in particular, that on the one hand the expensive coolers conventionally used in the past are eliminated and on the other hand the transient stresses in the axial area around which the cooling air flows are reduced. is there.

It is particularly advantageous that the cooling air on the rotor side for the turbine is recovered at the compressor boss behind the last rotor row of the compressor and the cooling air is swirled into the annular passage. The heating action of the rotor is minimized as much as possible by the cooling air and thus the level of transient stresses is also minimized. Further, by collecting on the boss side, high-purity air containing almost no dust is introduced into the annular passage.

It is furthermore advantageous if the pivot grid is arranged on the smallest radius in the annular passage and as close as possible to the impeller compartment. In this case, the minimum radius is adapted to the speed of sound produced at this local point. Thus, a means is provided for reducing axial thrust.

It is further advantageous that the labyrinth seal, which exerts a sealing action on the drum cover, is segmented on the rotor side in order to reduce the heat transfer coefficient α, so that the normally excessively high labyrinth seal in the labyrinth seal is obtained. The effect of the heat transfer coefficient α is cut off.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows only those components which are important for understanding the invention. Of the gas turbine installation, for example, the exhaust gas casing of a gas turbine having an exhaust gas pipe and a chimney and the inlet part of a compressor are not shown.
The direction of flow of the working medium is indicated by arrows.

The turbine 1 shown in FIG. 1 with only the first stage 2 axially flowing therethrough as a stator row and a rotor row comprises a rotor 3 and vanes approximately planted with blades. The inner casing 4 is suspended in a turbine casing 5.

In the embodiment shown, the turbine casing 5 has a collection chamber 6 for compressed air which is also compressed.
From the collection chamber 6, the combustion air reaches the interior of the annular combustion chamber 7, which communicates with the interior of the turbine, ie upstream of the first row of stator vanes. A compressor 9 is provided in the collection chamber 6.
Compressed air flows in from the diffuser 8.

Only the last stage 10 of the compressor is shown, in which case the vanes of this last stage consist of the original vanes and the trailing vanes. The rotor blades of the compressor and the turbine are engaged on a common shaft 11, the part occupying between the turbine and the compressor being configured as a drum 12.

The drum 12 is entirely surrounded by a drum cover 13 extending in the axial direction, and the drum cover 13 is fixed to a diffuser outer casing 15 of the compressor via ribs 14. The drum cover 13 forms a cover band for the blades of the last two compressor stationary blade rows on the compressor side.

On the turbine side, the drum cover 13 cooperates with the end face of the turbine rotor to extend radially in the impeller side chamber 1.
Seven. This impeller side chamber 17 forms the outflow end of an annular passage 18 which, starting from the boss behind the last compressor blade row, extends between the drum and the drum cover. Is running. The entire cooling air on the rotor side is introduced into the annular passage.

When designing an annular passage, the following must be considered based on the flow that generates a swirling flow that governs the inside of the annular passage. That is, in order to prevent the swirling flow from becoming unstable along the drum, the normal speed and tangential speed of the cooling air and the average passage radius and the average passage height are, as is well known based on the swirling flow theory, It must have a certain correlation.

A labyrinth seal 19 which exerts a sealing action on the drum cover at the end of the turbine is provided on the drum.
Is arranged. The labyrinth seal 19 seals against the drum cover only indirectly. The non-rotating part of the drum cover is fixed in the labyrinth body 24 in a suitable manner.

In order to reduce the heat transfer coefficient α, the labyrinth seal 19 is divided on the rotor side into a predetermined number of segments arranged on the drum surface. FIG. 3 shows the division of the labyrinth seal 19. In the embodiment shown, an axially extending hammerhead-shaped groove 21 is used, which is bored in a flange 22 of the drum 12.

A so-called heat-insulating segment is suspended in the groove 21 by appropriately formed legs 23. A metal sealing strip, not shown in FIG. 3, acts on the outer surface protruding into the annular passage of the heat insulating segment,
This sealing strip is, for example, pressed into the labyrinth body or otherwise fixed.

According to the invention, inside the annular passage 18, the cooling air is deflected in the swivel grid and accelerated to the highest tangential speed. The swirl grid 25 is provided as a swirl nozzle in the annular passage 18 directly against the end face 16 of the turbine rotor, ie
Communicates directly with the impeller side chamber 17. Advantageously, the turning grid is arranged on a minimum radius for reasons which will be explained in more detail below.

In order to hold the labyrinth body 24 in place, the labyrinth body 24 is connected to the drum cover 13 via a number of circumferentially distributed support ribs 26 which direct the flow.

FIG. 2 is an enlarged view showing the blades over the labyrinth body 24 in an expanded view of the cylindrical cross section. In this case, c means the absolute speed of the cooling air and u means the peripheral speed of the rotor. For sizing in the illustrated embodiment, the pitch to chord ratio is, for example, 1, 2 at the support rib 26 and approximately 0.8 at the swirl nozzle.
5

The support rib 26 is a flow rib having a symmetrical airfoil, in which case neither a change in the flow velocity nor a change in the flow direction occurs. The flow leaves the support ribs at velocity c and at an angle of approximately 20 degrees to the circumferential direction.

The swirl nozzle is an accelerating grid having an average birch line of small curvature, which deflects the flow from approximately 25 degrees to approximately 10 degrees and reduces the velocity to approximately 12 degrees.
Increase from 0 m / sec to almost 420 m / sec.

The mode of operation of the present invention will be described below based on several examples, but the disclosure of all absolute values based on calculations and experiments will be omitted. This absolute value is not sufficiently persuasive anyway based on the relevance of a very large number of parameters.

All the cooling air required to cool the rotor, ie approximately 8% of the compressed air, is recovered in the area of the boss behind the last row of blades. Annular passage 1
The cooling air generated by the swirling flow via 8 flows to a position short of the drum labyrinth seal.

The swirling flow pre-generated by the compressor results in a minimum heat transfer coefficient α and a minimum adiabatic wall temperature based on the small relative speed between the rotor surface and the cooling air. This results in low transient stresses and the lowest steady-state temperatures in the range.

Through the labyrinth seal 19, only the unacceptable leakage flows. It cannot be avoided that the tangential speed in the labyrinth seal 19 is reduced to approximately 50% of the peripheral speed. Therefore, a part of the above-described positive turning action is already lost. Furthermore, the value of the heat transfer coefficient α increases due to the inherent flow type in the labyrinth seal 19.

In this case, the protection is obtained by sectioning the labyrinth seal on the rotor side, whereby the heat flow into the drum is significantly reduced. Due to the fact that the swirling flow is reduced in the labyrinth seal, it is important to design the portion of the outflow passage 27 following the labyrinth seal as short as possible, ie to place the labyrinth seal as close as possible to the first turbine disk. is there.

The main part of the rotor cooling air is guided into the swirl nozzle 25 via support ribs 26 which direct the flow of the labyrinth body 24. In the swirl nozzle 25, the cooling air is accelerated to near the speed of sound while being slightly deflected simultaneously in the rotor rotation direction. In this case, the outflow from the swirl grid is almost tangential, that is, approximately 10
This is done at an angle in degrees.

On the one hand, this strong swirling flow has an advantageous effect on the heat transfer effect, as already mentioned. Advantageous values are obtained if the ratio of the tangential speed to the circumferential speed at the inlet of the cooling air into the rotor is approximately unity. This means that no work is exchanged when the rotor flows into the cooling passage, that is, no work is added to the rotor unless the work of the rotor is lost. In particular, the temperature of the cooling air is not raised by the pump operation.

Furthermore, due to the high speed levels, the static pressure at the outlet from the pivot grid is significantly reduced. Thus, a low average pressure prevails in the impeller chamber, which reduces the axial thrust of the rotor.

Of course, the invention is not limited to the embodiment shown. Therefore, instead of separately configuring the support ribs and the swirl nozzle, the support ribs and the swirl nozzle can be integrated into a single grid.

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view of a gas turbine.

FIG. 2 is an exploded view of a cylindrical section on an average diameter of an annular passage to be passed through.

FIG. 3 is a partial cross-sectional view of the drum in the plane of the labyrinth seal.

[Explanation of symbols]

1 turbine, 9 compressor, 12 drums, 13
Drum cover, 16 end faces, 18 annular passage, 1
9 Labyrinth seals, 20 segments, 25
Swivel grid

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-B-46-28059 (JP, B1) U.S. Pat. No. 3,208,084 (US, A) UK Patent Application Publication 2189845 (GB, A) Cl. ⁷ , DB name) F02C 7/18 F01D 5/08

Claims (3)

(57) [Claims] An axial-flow gas turbine having a multi-stage turbine (1) for driving a compressor (9) disposed on a common shaft (11), wherein a gas turbine is disposed between the turbine and the compressor. Is configured as a drum (12) surrounded by a drum cover (13) and is recovered from the compressor by an annular passage (18) formed between the drum and the drum cover. Cooling air is directed to the end face (16) of the turbine rotor and subsequently to a cooling passage on the rotor side of the turbine rotor, the pressure level at the compressor outlet and the cooling air into the turbine. A labyrinth seal (19) is provided on the drum for sealing against the drum cover in order to seal between the pressure level at the inlet of the turbine and a rotor for the turbine. In the type where the entire cooling air on the side is recovered from the compressor in the area of the compressor outlet, the cooling air on the rotor side for the turbine is recovered at the compressor boss behind the last bucket row of the compressor The cooling air is swirled into the cooling air and introduced directly into the annular passage, which is deflected inside the annular passage at the swirling grid (25) and close to the speed of sound. An axial-flow gas turbine, characterized in that the gas turbine is driven at a high speed. 2. An annular passage having a turbine side and an impeller side chamber (1).
7), characterized in that this impeller side chamber is limited on the one hand by the drum cover and on the other hand by the end face (16) of the turbine rotor,
The gas turbine according to claim 1. 3. The method according to claim 1, wherein the labyrinth seal for sealing the drum cover is divided into segments on the rotor side to reduce the heat transfer coefficient α. gas turbine.